In order to drill a new borehole that extends outside an existing cased wellbore in order to side track junk or drill toward another production target, the usual practice is to use a work string to run and set an anchored whipstock. If desired, a length of the casing where the whipstock is to be set is filled with cement, and a downhole motor and bit are used to drill a hole that deviates over to one side of the casing. After a whipstock has been set in the cemented region, a drill string and milling bits are used to cut out the window so that a new borehole that extends through the window can be drilled outside the casing. The anchor provides a platform that prevents downward movement of the whipstock whose deflection face is oriented at a desired azimuth prior to setting the anchor by rotating the work string at the surface. Then a starter mill on the lower end of the work string is used to cut an initial window through the casing wall opposite the deflection surface, and then the work string and starter mill are removed from the wellbore to allow a drill string having a window mill to be run in and rotated to enlarge the size of the window. Still another trip of the drill string typically is used to run a different type of window mill before the window through the side of the casing has been satisfactorily formed. This procedure requires multiple round trips of a running string to accomplish the desired objective, and thus is a time consuming and expensive operation. Moreover the reliability of prior systems in properly orienting the anchor so that the whipstock will be properly positioned has been less than desirable.
Such prior systems and tools have generally used a running string of tubing or drill pipe having individual joints or stands that must be threaded end-to-end as the tools are run into the well and then unthreaded as the tools are removed therefrom. Hereagain the procedure has been time consuming and expensive, particularly since multiple runs of the string have been required.
An object of the present invention is to provide new and improved methods and tool combinations for anchoring and orienting a whipstock in a well casing on a single trip of a running string into and out of the casing, thereby obviating the foregoing problems and disadvantages of prior systems.
Another object of the present invention is to provide new and improved methods and tool systems wherein a whipstock is oriented and anchored in a single trip of a running string and where orientation data is measured and transmitted to the surface substantially in real time to optimize setting reliability.
Still another object of the present invention is to provide new and improved methods and tools of the type described that are run on coiled tubing to provide significant overall cost savings for such operations.